1. Field of the Invention
The present invention relates to a servomotor controller for controlling a servomotor that uses as drive power, AC power obtained by converting AC power on the side of an AC power supply into DC power and further converting the DC power into AC power.
2. Description of the Related Art
In a servomotor controller for driving and controlling a servomotor in a machine tool, an industrial machine, a forging press, an injection molding machine, or each of various robots, AC power on the side of an AC power supply is temporarily converted into DC power, the DC power is further converted into AC power, and the AC power is used as drive power for a servomotor (to be referred to as a “drive axis servomotor” hereinafter) provided for each drive axis. Each drive axis in, for example, a machine tool is connected to a drive axis servomotor. The servomotor controller includes a converter circuit that converts AC power supplied from the side of an AC power supply serving as a commercial three-phase AC power supply into DC power and outputs the DC power, and an inverter circuit that is connected to a DC link on the DC side of the converter circuit and performs power conversion between DC power in the DC link and AC power serving as the drive power or regenerative power of a motor, and the servomotor controller controls the velocity, torque, or rotor position of a servomotor connected to the AC side of the inverter circuit.
Upon acceleration or deceleration control of the motor by the servomotor controller, a power peak occurs because the output or regeneration of high AC power may be preferably performed in the AC power supply. Under the circumstances, it is a common practice to design a power supply equipment capacity on the side of an AC power supply that supplies power to the servomotor controller, in consideration of the power peak occurring upon acceleration or deceleration of the motor. However, in design that takes into consideration the power peak occurring upon acceleration or deceleration of the servomotor, the power peak is inevitably high compared to those in design in which the average power of the servomotor controller is simply taken into consideration. Especially in a servomotor controller that is more likely to rapidly accelerate or decelerate a servomotor, the power peak is accordingly higher. Since the higher the power peak, the higher the installation and operation costs, the power peak is desirably reduced.
To reduce the power peak, a method for providing an energy storage device that may store DC power in a DC link connecting a converter circuit and an inverter circuit of a servomotor controller to each other to appropriately exchange energy consumed or regenerated in each servomotor via the DC link has been conventionally employed. With this method, appropriate control of each amount of power conversion in a powering operation (conversion operation) for converting AC power into DC power and a power regeneration operation (inversion operation) for converting DC power into AC power by the inverter circuit can store in the energy storage device, regenerative power generated by the servomotor in deceleration of the servomotor, and reuse the stored power in acceleration of the servomotor, so that the power peak can be reduced.
FIG. 7 is a block diagram illustrating an exemplary conventional servomotor controller including buffer axis servomotors of a single-winding type as an energy storage device to reduce the power peak. A servomotor controller 1000 that drives two drive axis servomotors 2A-1 and 2A-2 will be described below as an example.
A servomotor normally includes at least one winding and one inverter circuit may be preferably provided per winding in a servomotor to drive the servomotor. FIG. 7 illustrates each of servomotors 2A-1, 2A-2, 2B-1, and 2B-2 as the single-winding type as an example. An inverter circuit 112-1 is provided to supply drive power to the drive axis servomotor 2A-1 to drive and control the drive axis servomotor 2A-1, and an inverter circuit 112-2 is provided to supply drive power to the drive axis servomotor 2A-2 to drive and control the drive axis servomotor 2A-2.
Converter circuits (reference numerals 111-1 and 111-2) are provided in correspondence with the inverter circuits 112-1 and 112-2 in the example illustrated in FIG. 7, but only one converter circuit may be provided for a plurality of inverter circuits in order to keep the cost and occupied space of the servomotor controller 1000 less. The converter circuit 111-1 converts AC power supplied from an AC power supply 3 and outputs DC power, and the inverter circuit 112-1 converts the DC power output from the converter circuit 111-1 into AC power to be supplied as drive power for the drive axis servomotor 2A-1 and converts AC power regenerated from the drive axis servomotor 2A-1 into DC power. The converter circuit 111-2 converts AC power supplied from the AC power supply 3 and outputs DC power, and the inverter circuit 112-2 converts the DC power output from the converter circuit 111-2 into AC power to be supplied as drive power for the drive axis servomotor 2A-2 and converts AC power regenerated from the drive axis servomotor 2A-2 into DC power.
To reduce the power peak, an energy storage device 120 that can store or supply DC power is provided to a DC link connecting the converter circuit 111-1 and the inverter circuit 112-1 to each other and a DC link connecting the converter circuit 111-2 and the inverter circuit 112-2 to each other. FIG. 7 illustrates as an example, an energy storage device 120 including servomotors (to be referred to as “buffer axis servomotors” hereinafter for the sake of distinction from drive axis servomotors) 2B-1 and 2B-2 and inverter circuits 112-3 and 112-4 provided in correspondence with the respective buffer axis servomotors. In other words, the DC link connecting the converter circuit 111-1 and the inverter circuit 112-1 to each other is provided with an inverter circuit 112-3 for mutual conversion between electrical energy in the DC link and rotational energy of the buffer axis servomotor 2B-1, and the DC link connecting the converter circuit 111-2 and the inverter circuit 112-2 to each other is provided with an inverter circuit 112-4 for mutual conversion between electrical energy in the DC link and rotational energy of the buffer axis servomotor 2B-2.
When, for example, the drive axis servomotor 2A-1 decelerates, regenerative power occurs, and the DC link voltage between the converter circuit 111-1 and the inverter circuit 112-1 rises, the DC power in the DC link is converted by the inverter circuit 112-3 into AC power, which is used as power to accelerate the buffer axis servomotor 2B-1. With this operation, electrical energy in the DC link can be stored as rotational energy of the buffer axis servomotor 2B-1. Further, when, for example, the drive axis servomotor 2A-1 accelerates and the DC link voltage between the converter circuit 111-1 and the inverter circuit 112-1 drops, decelerating the buffer axis servomotor 2B-1 produces AC regenerative power, which is converted into DC power by the inverter circuit 112-3. Even when the DC link voltage between the converter circuit 111-2 and the inverter circuit 112-2 rises or drops upon acceleration or deceleration of the drive axis servomotor 2A-2, the inverter circuit 112-4 is similarly operated, so that energy can be stored in the buffer axis servomotor 2B-2 or energy can be supplied from the buffer axis servomotor 2B-2 to the DC link. Respective electrical energies obtained by conversion from the rotational energies of the buffer axis servomotors 2B-1 and 2B-2 can be reused in acceleration of the drive axis servomotors 2A-1 and 2A-2, respectively, to reduce the power peak in the entire servomotor controller 1000.
FIG. 8 is a block diagram illustrating an exemplary conventional servomotor controller for driving a plurality of axes, including buffer axis servomotors of a plural-winding type as an energy storage device to reduce the power peak. The example illustrated in FIG. 8 assumes that a servomotor controller 1001 includes four drive axis servomotors 2A-1, 2A-2, 2A-3, and 2A-4, the drive axis servomotors 2A-1 and 2A-2 are used to drive a first drive axis (not illustrated), and the drive axis servomotors 2A-3 and 2A-4 are used to drive a second drive axis (not illustrated), independently of the first drive axis. The drive axis servomotors 2A-1, 2A-2, 2A-3, and 2A-4 are provided with a pair of a converter circuit 111-1 and an inverter circuit 112-1, a pair of a converter circuit 111-2 and an inverter circuit 112-2, a pair of a converter circuit 111-3 and an inverter circuit 112-5, and a pair of a converter circuit 111-4 and an inverter circuit 112-6, respectively. Since the first drive axis and the second drive axis are independently driven, an energy storage device (denoted by reference numerals 121 and 122) is provided in correspondence with each drive axis. When buffer axis servomotors for each of the energy storage devices 121 and 122 are implemented as a single unit, buffer axis servomotors of the two-winding type (denoted by reference numerals 2B-3 and 2B-4) are used, as illustrated in FIG. 8. Inverter circuits 112-3, 112-4, 112-7, and 112-8 are provided in correspondence with the buffer axis servomotors 2B-3 and 2B-4 of the two-winding type. Electrical energy obtained by conversion from the rotational energy of the buffer axis servomotor 2B-3 can be reused in acceleration of the drive axis servomotors 2A-1 and 2A-2, and electrical energy obtained by conversion from the rotational energy of the buffer axis servomotor 2B-4 can be reused in acceleration of the drive axis servomotors 2A-3 and 2A-4 to reduce the power peak in the entire servomotor controller 1001.
A servo press is available which is supplied with power from a flywheel storage device in accordance with the power requirement to avoid an excessive power supply peak requirement, as disclosed in, for example,
Japanese Unexamined Patent Publication (Kokai) No. 2008-23599.
A motor drive device is also available which includes both a capacitor storage unit and a flywheel storage unit as an energy storage device and stores or supplies energy using the capacitor storage unit, the flywheel storage unit, or both of them as appropriate, as disclosed in, for example, Japanese Unexamined Patent Publication (Kokai) No. 2013-9524.
Another servo press is available which includes a power supply circuit capable of mutual regenerative power supply between a main motor amplifier and a conveyor motor amplifier, as disclosed in, for example, Japanese Unexamined Patent Publication (Kokai) No. 2009-285666.
Further, in a press facility, a configuration is available which connects a servo press power converter and a machine press power converter to an AC link, generates regenerative power using a machine press and supplies it to a servo press when the servo press involves high power, as disclosed in, for example, Japanese Unexamined Patent Publication (Kokai) No. 2010-221221.
A motor drive device is known which uses a secondary battery, a large-capacity power capacitor, an electric double-layer capacitor, or the like as an energy storage device, as disclosed in, for example, Japanese Unexamined Patent Publication (Kokai) No. 2009-136058.
In the conventional method for reducing the power peak by appropriately exchanging energy consumed or regenerated in each of the above-mentioned servomotors via the buffer axis servomotors provided to the DC links, a buffer axis servomotor and an inverter circuit therefor may be preferably provided in correspondence with a pair of a converter circuit and an inverter circuit for a drive axis servomotor. Therefore, when a plurality of drive axis servomotors are present, a plurality of pairs of buffer axis servomotors of the single-winding type and inverter circuits therefor may be preferably provided in correspondence with the number of drive axis servomotors, or a pair of a buffer axis servomotor of the plural-winding type including windings corresponding in number to drive axis servomotors and an inverter circuit therefor may be preferably provided.
When a buffer axis servomotor of the single-winding type is provided as illustrated in, for example, FIG. 7, a buffer axis servomotor 2B-1 and an inverter circuit 112-3 may be preferably provided to a pair of a converter circuit 111-1 and an inverter circuit 112-1 for a drive axis servomotor 2A-1, and a buffer axis servomotor 2B-2 and an inverter circuit 112-4 may be preferably provided to a pair of a converter circuit 111-2 and an inverter circuit 112-2 for a drive axis servomotor 2A-2. This poses a problem that the number of pairs of buffer axis servomotors of the single-winding type and inverter circuits therefor increases, thus inevitably involving a higher cost and larger device.
When a first drive axis and a second drive axis are driven as illustrated in, for example, FIG. 8, an energy storage device 121 and 122 is provided in correspondence with each drive axis to reduce the power peak. Since the buffer axis servomotors 2B-3 and 2B-4 of the energy storage devices 121 and 122, respectively, independently accelerate or decelerate in accordance with the drive states of the first drive axis and the second drive axis, the power peak can be reduced in the servomotor controller 1001 as a whole. However, since an energy storage device may be preferably provided for each drive axis, a problem is posed that the number of energy storage devices increases, thus inevitably involving a higher cost and larger device.
In this manner, the conventional method poses a problem that an attempt to reduce the power peak inevitably involves a higher cost and larger device.